"Unknown field" after updating to 3.5.0 marshmallow

Question

Updated dependency in my project

Before

marshmallow-sqlalchemy==0.17.0
marshmallow==3.0.0b6

After

marshmallow-sqlalchemy==0.21.0
marshmallow==3.5.0

I have such a model (simplified):

from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class MyModel(Base):
    __tablename__ = 'my_model'

    id = Column(BigInteger, primary_key=True)
    field_name = Column(String)
    password = Column(String)

And schema:

from marshmallow import fields
from marshmallow_sqlalchemy import (
    ModelSchema,
    field_for,
)
class RegistrarSchema(ModelSchema):
    class Meta:
        model = MyModel

    other_field_name = fields.Function(lambda obj: obj.field_name)
    field_name = field_for(MyModel, 'field_name', load_from='other_field_name')

    password = fields.Method("get_password")

    def get_password(self, obj):
        return decrypt_password(obj)

    def load(self, data, session=None, instance=None, transient=False, *args, **kwargs):
        if 'password' in data:
            password = data['password']
            instance = encrypt_password(password, instance)
        return super(ModelSchema, self).load(
            data, *args, session=session, instance=instance,
            transient=transient, **kwargs
        )

And using this code i could call

RegistrarSchema.load(data={'other_field_name': 'my_value'}, instance=instance, session=session)

and this value would be saved to field_name in my database.

After update i lost this functional - now i get

File "myfile.py", line 116, in load
    transient=transient, **kwargs
  File "/usr/local/lib/python3.7/dist-packages/marshmallow_sqlalchemy/schema.py", line 214, in load
    return super().load(data, **kwargs)
  File "/usr/local/lib/python3.7/dist-packages/marshmallow/schema.py", line 723, in load
    data, many=many, partial=partial, unknown=unknown, postprocess=True
  File "/usr/local/lib/python3.7/dist-packages/marshmallow/schema.py", line 904, in _do_load
    raise exc
marshmallow.exceptions.ValidationError: {'other_field_name': ['Unknown field.']}

And exaclty same error when updating password -

RegistrarSchema.load(data={'password': 'my_value'}, instance=instance, session=session)

I didnt write this code myself and cant contact developer who did it.

As i get it the goal for the first case is to give ability to write in both way -data={'my_field': 'value'} and data={'other_field_name': 'value'}. First scenario still working on new version, but the second not.

And in case with password - goal is to make serialization/deserialization more complex with encrypting/decrypting data.

I read update notes but was not able to find anyting specific to this issue, can someone help?

Answer 1

In v3., marshmallow changed the default behavior from EXCLUDE to RAISE https://marshmallow.readthedocs.io/en/stable/quickstart.html#handling-unknown-fields.

You can revert to the old behavior by specifying unknown in the class Meta of your Schema:

from marshmallow import EXCLUDE
class UserSchema(Schema):
    class Meta:
        unknown = EXCLUDE

at instantiation time,

schema = UserSchema(unknown=EXCLUDE)

or when calling load.

UserSchema().load(data, unknown=EXCLUDE)

The unknown option value set in load will override the value applied at instantiation time, which itself will override the value defined in the class Meta.